<header>
    <nav>
        <style>
            /* 导航栏样式 */
        nav {
            background-color: #2478cb;
            padding: 10px 0;
        }

        nav ul {
            list-style-type: none;
            margin: 0;
            padding: 0;
            display: flex;
            justify-content: center;
        }

        nav li {
            margin: 0 15px;
        }

        nav a {
            color: white;
            text-decoration: none;
            font-size: 18px;
            transition: color 0.3s ease;
        }

        nav a:hover {
            color: #007bff;
        }

        </style>
        <ul>
            <li><a href="/">首页</a></li>
            <li><a href="/book">图书管理</a></li>
            <li><a href="/user">用户管理</a></li>
        </ul>
    </nav>
</header>